The present disclosure relates to multilateral wells in the oil and gas industry and, more particularly, to improved torque supports for mill and whipstock assemblies used to drill multilateral wells.
Hydrocarbons can be produced through relatively complex wellbores traversing a subterranean formation. Some wellbores can be a multilateral wellbore, which includes one or more lateral wellbores that extend from a parent or main wellbore. Multilateral wellbores typically include one or more windows or casing exits defined in the casing that lines the wellbore to allow corresponding lateral wellbores to be formed. More specifically, a casing exit for a multilateral wellbore can be formed by positioning a whipstock in a casing string at a desired location in the main wellbore. The whipstock is often designed to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) machines away and eventually penetrates part of the casing to form the casing exit through the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore.
Single-trip whipstock designs allow a well operator to run the whipstock and the mills downhole in a single run, which greatly reduces the time and expense of completing a multilateral wellbore. Some conventional single-trip whipstock designs anchor a lead mill to the whipstock using a combination of a shear bolt and a torque lug. The shear bolt is designed to shear upon assuming a particular set down weight when a well operator desires to free the mills from the whipstock. The shear bolt is typically not designed to shear in torque. The torque lug, on the other hand, provides rotational torque support that helps prevent the shear bolt from fatiguing prematurely or otherwise shearing in torque as the whipstock is run into the main wellbore. The lead mill provides a slot that the torque lug fits into to prevent the lead mill from rotating about its central axis. In this configuration, however, the lead mill may nonetheless be able to pivot on the torque lug and one of its blades contacting the ramped surface of the whipstock, which creates a lift force that puts the shear bolt in tensile and torsional stress. This can fatigue the shear bolt and causes it to shear prematurely, thereby prematurely freeing the lead mill from whipstock.